The present invention relates to metallurgy and, more particularly, it relates to foundry apparatus, namely, to casting molds for casting by squeezing, particularly for the casting of large size thin-walled objects having an intricate form, such as a space casings and panels with ribbing and local bosses. The present invention can be most extensively used in the manufacture of very critical parts, mainly in aircraft, which should be manufactured from a cast material of stable and high quality.
In the last decade, the so-called method of casting by squeezing has found extensive application for producing large-size thin-walled (2-5 mm) castings whose thickness corresponds to that of the finished part. This method involves a synchronous drawing together of half molds, forming a split mold, to ensure the displacement from the bottom zone of the mold or metal receiver cavity of a greater part of liquid metal, poured therein, into the top zone of a communicating cavity in the center of which the casting proper is formed while at the edges, in places of separation of the half molds, flat slit gates are formed communicating with the body of the casting.
The rate of the metal level rise in the mold is an important parameter of the casting process, and is responsible for quality crystallization of metal in the mold upon the drawing together of the half molds and, as a result, for the high quality of the material of the thus produced casting. The rate at all of the stages of the formation of casting should not exceed a given critical value depending upon a number of factors, including the type of metal and initial temperature thereof. In order to ensure the optimum rate of the rise of the metal level in the mold, the half molds are drawn together at a variable rate which, in turn, depends upon the variation of the mold cavity cross-section.
For casting by squeezing, use is made of casting molds having a base with a core centrally mounted thereon, the outer surface of the core corresponding to the inner surface of the blank. The half molds are also mounted on the base with the ability to move towards each other so as to be drawn together to form the mold and subsequently for being drawn apart to effect the splitting of the mold. The working or inner surfaces of the half molds correspond to the outer contours of the casting being formed. The surface of the base and of the bottom portion of the half molds form a metal receiver into which a batch of liquid metal is poured from which to form the casting. The gaps between the half molds are closed over their periphery in the mold splitting zone, prior to pouring the metal into the metal receiver and during the time of forming a casting, with compression cheeks stationarily mounted or movable together with one of the half molds. These gaps serve as the slit gates of the mold (cf., V. N. Vinogradov, Liteiniye formy dlia tsvetnykh splavov--Casting Molds for Non-Ferrous Alloys, Mashinostroiyeniye Publishers, Moscow, 1981, pp. 35, 37).
When using such half molds in a machine for casting by squeezing, the base of a split casting mold is secured on the central portion of the machine frame, while there is mounted at the edges of the frame posts with plates to which the half molds are securely attached and which are capable of moving with the aid of individual drives for drawing apart and splitting the mold. For example, in the case of a hydraulic drive for moving the plates, which is used most frequently in machines of this type, the latter are provided with means for synchronization of the movement of the plates and programmable adjustment of their rate of movement. The rate of movement of the plates is varied by varying the flow section of pipelines supplying said drives, by way of directional control from followers over the position of special throttle units built in the pipelines. The working profile of such followers is calculated or selected empirically such as to ensure a specific mode of half mold movement to make up a split mold for forming a specific casting only. The presence of intermediate links in the follower-throttle unit-drive-plate system results in some deviation from the preset mode of the half mold movement in the course of forming a casting. Such deviation is further aggravated by the fact that the follower profile cannot be given a shape that would ideally satisfy the condition of ensuring the rated mode of half mold movement with abrupt and substantial angular variations of casting profile portions since the conditions of force interaction of the follower with the element transmitting the control displacement to the slide valve of the throttle unit define the maximum permissible direction angle of the follower profile which should not exceed the pressure angle for the transmitting mechanism, which angle normally does not exceed 45.degree.. The afore-listed problems affect the maintance of the accuracy of the mode of half mold movement and is characterized by a relatively stable nature are complemented with those of an unstable nature for which it is relatively difficult or just impossible to introduce timely corrections in devices presetting the mode of movement. Such complementary problems include, for instance, variations in the viscosity of the working fluid in the hydraulic system of the machine in the course in the operation causing some variation of dynamic characteristics of the power drive; the instability of variation of the viscosity of metal in the mold cavity in the course of forming a casting. In addition some instability of the values of cross-sectional area of the mold cavity occurs between the half molds being drawn together at one and the same value of the mold stroke and at one and the same level, due to the instability of thickness of refractory coating applied to the half mold surfaces forming the casting periodically after pouring the metal or after a cycle of such pourings.
As a result, passive control over the mode of movement of half molds by their drives in the course of forming a casting for maintaining optimal rate of the use of metal surface level in the mold using a follower alone, as practiced in prior art machines, brings about a situation where the rate of the rise of metal surface level in the mold cavity differs in most cases from the rated one and, in some portions of the casting where such rate exceeds the maximum permissible one, there is observed a marked deterioration of the quality of cast metal manifested as a sharp violation of the homogeneity of the structure, poorer mechanical properties of the material in such portions, increased surface roughness and porosity, emergence of cavities, microcracks etc.
It is an object of the present invention to develop a split casting mold for use in a casting machine having an adjustable drive for moving the plates, wherein the half molds would be provided with the possibility of affecting the metal at preselected levels of the mold while ensuring local correction of the rate of said metal level rise.
It is another object of this invention to develop a casting mold that would ensure an improved rate of the rise of level of metal in the mold.
Other objects of the present invention include ensuring with the mold of the invention a high stability of the mode of forming the portion of casting which actually represents the cast blank of a part, as well as ensuring an improved quality of cast metal of such a cast blank and a high stability of such improved quality over the blank length and in different blanks.